Western pipistrelles sometimes leave their roosts before sundown and can be mistaken for late-flying butterflies, because they are so tiny and fly slowly and erratically, with much fluttering of their wings. Most common at low elevations in desert scrub and arid grassland habitats, they are also found in adjacent woodlands. Learn more about the Pipistrellus hesperus, more commonly known as a Western Pipistrelle, in this easy-to-read species overview by the Smithsonian's National Museum of Natural History.